US Patent 7721938 Friction stirring-joining method and method of manufacturing hollow body

A friction stir welding method in which a base having a recess, and a cover for fitting into and closing the opening of the recess are prepared. A stepped portion on the inner circumferential surface of the recess at an intermediate depth allows a peripheral portion of the cover to rest thereon. A cylindrical holder portion having a cooling-medium accommodation recess is formed integrally with the outer surface of the cover. The cover is fitted into the recess and placed on the stepped portion. A cooling medium is placed in the cooling-medium accommodation recess. A friction-stir-welding tool probe is plunged into a peripheral portion of the base around an opening of the recess and into a peripheral portion of the cover. During rotation of the probe, the base, and the cover, and the probe undergo relative movement, friction-stir-welding the base and the cover together.